1. Field of the Invention
The present invention relates to a single-particle mass spectrometer, and more particularly to an improved single-particle mass spectrometer capable of reducing a loss caused by a collision between a flying ion and a wall of a flying tube and thus improving a measuring efficiency of an ion detector by enhancing an ion focusing efficiency.
2. Description of the Related Art
Generally, a single-particle mass spectrometer analyzes aerosol of solid or liquid materials floating in the atmosphere so as to measure a pollution level of the atmosphere. A conventional single-particle mass spectrometer is operated in a way that, if aerosol is put into a chamber that is in a vacuum state by a vacuum pump, aerosol particles are accelerated to a chamber center due to the pressure difference and at the same time focused by an aerodynamic lens.
The aerosol particles focused by the aerodynamic lens are ionized again since a laser beam is irradiated thereto, and these ions are extracted and accelerated again and then input to a detector after flying along a cylindrical flying tube at a uniform velocity.
A conventional spectrometer includes a flat reflector to which a high voltage is applied, ion extraction grids having a mesh shape arranged in parallel with the flat reflector, and an ion acceleration grid mostly grounded. Ions are extracted due to the voltage difference between the flat reflector and the ion extraction grids, are accelerated due to the voltage difference between the ion extraction grids and the ion acceleration grid, and then fly at different speeds depending on ion masses but at a uniform velocity in the flying tube that is kept in an electrically neutral state. But there is a problem that trajectories of the ions radially emitted by laser are not focused but mostly collided with the inner wall of the flying tube and then disappeared.
In addition, if an initial kinetic energy of emitted ions is greater, more ion losses are caused. For example, in case the composition of a single particle is irregular inside the particle in a radial direction like a particle having a core-shell structure, ions generated in the particle have different kinetic energy from ions generated from the surface, and thus their measuring efficiencies are changed, which may make the ions on the surface be underestimated.
In particular, the detector generally has a small size not greater than about 25 mm, so a proportion of ions reaching the detector is very low. In fact, in case an initial kinetic energy of ions is 100 eV, it was shown that a measuring efficiency is very low, less than 1%.